The invention relates to a control device for an electric machine or an electric motor, in particular a control device in the form of a frequency converter or of a servo-controller.
The invention is based on the object of making available a control device for an electric motor which can, when necessary, bring about a safe, torque-free state of an electric motor, in particular a field-weakened electric motor.
The control device according to the invention, for example in the form of a frequency converter, serves to actuate an electric machine, in particular an electric motor. The electric motor may be, for example, a conventional synchronous machine or an asynchronous machine.
The control device has a motor control unit which is designed to generate a number of motor control signals. The number of motor control signals may be, for example, six or more than six.
The control device also has a safety unit which is independent of the motor control unit and is designed to generate a number of safety control signals. The number of safety control signals may be, for example, four or more than four. The safety unit can be designed to monitor operation of a drive system which contains the control device and the electric motor. For this purpose, a suitable sensor system may be provided. In the case of the safety unit detecting a critical or faulty state, the safety unit generates the safety control signals in such a way that a state which is as safe as possible, in particular a torque-free or torque-reduced state independently of the motor control signals which are generated by the motor control unit.
The control device also has a driver unit which is supplied with the motor control signals and the safety control signals and which is designed to generate power semiconductor control signals for associated power semiconductors of a conventional inverter unit.
The control device also has the inverter unit with a number of bridge branches. The number may be, for example, three. The bridge branches are conventionally supplied with a positive intermediate circuit potential at a first end, and with a negative intermediate circuit potential at a second end. The bridge branches each have a bridge output terminal and each have two or more power semiconductors which are actuated by an associated power semiconductor control signal of the power semiconductor control signals. The power semiconductors may be, for example, IGBTs.
The driver unit is designed to generate, irrespective of a state of the motor control signals in the case of a first state pattern of the safety control signals, the power semiconductor control signals in such a way that all the power semiconductors have a non-conductive state. In other words, all the power semiconductors are switched off, with the result that safe torque enabling occurs.
The driver unit is also designed to generate, irrespective of a state of the motor control signals in the case of a second state pattern of the safety control signals, which is different from the first state pattern, the power semiconductor control signals in such a way that a respective bridge output terminal of all the bridge branches is electrically connected to the positive intermediate circuit potential. The second state pattern or the associated power semiconductor control signals may serve, for example, to safely reduce the torque or enable the torque of a field-weakened machine in the field-weakening range without an intermediate circuit being charged to an excess voltage via associated free-wheeling diodes of the power semiconductors, with the result that, for example, damage to the devices which are coupled to the intermediate circuit can be avoided. At the same time it is ensured that in this state no unacceptably large torque is generated.
The driver unit is also designed to generate, irrespective of a state of the motor control signals in the case of a third state pattern of the safety control signals, which is different from the first or second state pattern, the power semiconductor control signals in such a way that a respective bridge output terminal of all the bridge branches is electrically connected to the negative intermediate circuit potential. This state corresponds functionally to second state pattern.
The driver unit can also be designed, in the case of a fourth state pattern of the safety control signals, to generate the power semiconductor control signals as a function of the motor control signals. The power semiconductor control signals can correspond to the motor control signals here.
Given the presence of the first, second and third state pattern of the safety control signals, the power semiconductor control signals are generated independently of the motor control signals, i.e. the safety control signals or the state patterns thereof overwrites the motor control signals, with the result that a torque-free state can be forcibly brought about, for example by a suitable state pattern of the safety control signals, even if the motor control signals are generated by the motor control unit for generating a torque which is different from zero. The fourth state pattern of the safety control signals can correspond to an enabled state during which the motor control signals determine the generation of the power semiconductor control signals.
The bridge branches can each have more than two power semiconductors which are actuated by an associated power semiconductor control signal of the power semiconductor control signals. For example it is possible to provide four power semiconductors per bridge branch, which power semiconductors are correspondingly assigned four power semiconductor control signals. This permits multi-stage operation of a respective bridge branch.
The control device can have a first voltage supply unit and a second voltage supply unit which is independent of the first voltage supply unit. The first voltage supply unit can be designed to supply the motor control unit and/or the safety unit and/or the driver unit or respective components thereof with an operating voltage. The second voltage supply unit can additionally be designed to supply the motor control unit and/or the safety unit and/or the driver unit or respective components thereof with an operating voltage, with the result that the operating voltage supply is configured in a redundant fashion for safety reasons.
The driver unit can have a first group of functional elements (driver, digital logic, analog circuit etc.) which are designed to generate power semiconductor control signals for those power semiconductors which are connected between the positive intermediate circuit potential and the bridge output terminal, and have a second group of functional elements which are designed to generate power semiconductor control signals for those power semiconductors which are connected between the negative intermediate circuit potential and the bridge output terminal. The first voltage supply unit can be designed to supply the first group and/or the second group with an operating voltage, and the second voltage supply unit can be designed to supply the first group and/or the second group with an operating voltage, with the result that the operating voltage supply is configured in a redundant fashion for safety reasons, and a safe state can be set even when one of the supply voltages fails.
The control device can have a switching unit which is electrically connected on the input side to the first and the second voltage supply units and which is electrically connected on the output side to the motor control unit, the safety unit and the driver unit, wherein the switching unit is designed, in the event of one of the voltage supply units being defective, to output the operating voltage of the non-defective voltage supply unit on the output side and to supply the motor control unit, the safety unit and the driver unit or components thereof with the operating voltage which is output.
The control device can have sensors, for example in the form of rotational speed sensors, current sensors, voltage sensors, temperature sensors etc., which are coupled to the safety unit and which are designed to measure measurement variables in the form of a rotational speed of the electric motor, an intermediate circuit voltage, one or more current measurement signals and/or one or more motor signals. The sensors can additionally also be coupled to the motor control unit. The safety unit can be designed to generate the state patterns of the safety control signals as a function of the measurement variables. The safety unit can be designed to generate the state patterns of the safety control signals additionally or alternatively as a function of a model calculation. By means of the model calculation it is possible, for example, to determine a motor rotational speed indirectly.
The safety unit can be designed to generate the first state pattern of the safety control signals below a threshold rotational speed, and to generate the second or the third state pattern of the safety control signals above the threshold rotational speed.
In a basic rotational speed range below the threshold rotational speed, when necessary the power semiconductors are switched off by the safety unit. Since a peak value of a motor voltage is typically below the intermediate circuit voltage here, a motor current drops and the machine is free of torque.
Instead, above the threshold rotational speed the lower group of the power semiconductors (those power semiconductors which are connected between the negative intermediate circuit potential and the bridge output terminal) or the upper group of the power semiconductors (those power semiconductors which are connected between the positive intermediate circuit potential and the bridge output terminal) is switched on, and therefore the electric motor is short-circuited. Electric motors which can be field-weakened can be dimensioned in such a way that they have a short-circuit current (torque) which is below the rated current (rated torque) of the electric motor. Therefore, this state does not constitute an overload of the power semiconductors.
There is also the possibility of switching on the lower and upper group of the power semiconductors alternately, wherein a switching frequency is preferably kept low, in order to keep corresponding switching losses low.
It is also possible, in the case of one of these two deactivation paths failing, to switch on the respective other group of power semiconductors. The failure (open circuit) can be detected, for example, from the rising of the intermediate circuit voltage.
The safety unit can be designed to determine, as a function of the measurement variables, whether one or more of those power semiconductors which electrically connect the bridge output terminal to the positive or negative intermediate circuit potential are defective, for example cannot be switched on (made conductive) or cannot be switched off (made non-conductive). For this purpose, for example, current sensors can be provided at a suitable location in the bridge branch, which current sensors permit the safety unit to compare an actual current with a current which is to be expected according to a switched state of the power semiconductors.
The safety unit can be designed to determine, as a function of the measurement variables, whether one or more of those power semiconductors which electrically connect the bridge output terminal to the positive intermediate circuit potential cannot be switched on (made conductive), wherein if this is the case the first or the third state pattern of the safety control signals is generated.
The safety unit can also be designed to determine, as a function of the measurement variables, whether one or more of those power semiconductors which electrically connect the bridge output terminal to the positive intermediate circuit potential cannot be switched off (made non-conductive), wherein if this is the case the first or the second state pattern of the safety control signals is generated.
The safety unit can also be designed to determine, as a function of the measurement variables, whether one or more of those power semiconductors which electrically connect the bridge output terminal to the negative intermediate circuit potential cannot be switched on, wherein if this is the case the first or the second state pattern of the safety control signals is generated.
The safety unit can also be designed to determine, as a function of the measurement variables, whether one or more of those power semiconductors which electrically connect the bridge output terminal to the negative intermediate circuit potential cannot be switched off, wherein if this is the case the first or the third state pattern of the safety control signals is generated.
The safety unit can be designed to determine, as a function of the measurement variables, whether a short circuit is present within one or more bridge branches, wherein if this is the case an associated state pattern of the safety control signals is generated.
The safety unit can be designed to generate, in particular on the basis of the first state pattern of the safety control signals, the second or third state pattern of the safety control signals if the intermediate circuit voltage exceeds a threshold value, in order in this way to prevent a further rise in the intermediate circuit voltage.
The safety unit can be designed, in the case of the safety control signals being generated with the second or third state pattern, to generate a state pattern which is different from the second or third state pattern if a measurement variable in the form of a motor current exceeds a threshold value, in order to reduce the motor current.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.